Nabil M. Lawandy

Relaxation oscillations in optically pumped molecular lasers

We report the observation of relaxation oscillations in both the C13H 3 F and C12H 3 F optically pumped lasers. Expressions are derived for the oscillation frequency and its temperature and pressure dependences using a four-level rate equation model. We observe excellent agreement between measured frequencies and the theory presented. Models are considered for using this phenomenon to determine the rotational and vibrational relaxation mechanisms of the laser gases.

Pressure shift in the 170-μm emission of the cw optically pumped CH 3 OH laser

Pressure shifts of +15 MHz/Torr were observed in 168–167 170-μm cw CH3OH optically pumped laser emission. The experiments were performed using a harmonic mixing technique in a Schottky diode. The results are explained in terms of a second-order dipole–dipole interaction in a statistical formulation.

Temperature dependence of optically pumped far-infrared (FIR) laser output power

The temperature dependence of the small signal gain and saturation power are derived using temperature-dependent rates in a four-level model. An expression is developed for the output power of a far-infrared oscillator as a function of temperature for both fixed pressure and fixed density. The results are valid in the regime of homogeneous broadening of the rotational transition and Doppler broadening of the pump transition. It is shown that, for most lasers, both the small signal gain and the saturation power decrease with increasing temperature. These effects have the overall result of increasing output power with decreasing temperatures.

Distributed feedback modes in a partially filled ring cavity

We have studied the threshold longitudinal modes of a structure composed of a ring cavity partially filled with a distributed feedback (DFB) medium. An eigenvalue equation and dispersion relation for the propagation constant, threshold gain, and mode location are derived and numerically solved for a number of cases. We show that the incommensurate nature of the unfilled ring cavity eigenfrequencies and DFB eigenfrequencies can lead to an enhancement of the frequency selectivity of the distributed feedback laser. The analysis is extended to consider finite linewidth and dispersion.

Double-resonance study of vibrational equilibration in optically pumped laser molecules

A cw frequency-locked CO2 laser is used in conjunction with a 1-J TEA CO2 laser to observe the vibrational equilibration of optically pumped gases. Velocity-dependent effects in the vibrational-deactivation rate are also observed. Experimental results are given for CH3F.

Collisional narrowing by polyatomic buffer gases in an optically pumped CH3F laser

The gain linewidth of an optically pumped CH3F molecular laser is observed to narrow with the addition of various polyatomic buffer gases. This is interpreted as collisional (Dicke) narrowing. The measurement is the first observation of collisional narrowing by polyatomic buffer gases. It is also the first observation of the effect in a laser oscillator. The effect was observed using a heterodyne mixing technique at the laser emission frequency of 604 GHz. Collision cross sections for SF6–CH3F and CS2–CH3F are obtained.

Approximate analytic solutions for the optical pumping of fluorescent dyes

A general technique for solving a system of rate equations describing the interaction of an electromagnetic field and a molecular system is presented. The method is used to obtain approximate time-dependent solutions for the upper-level populations of fluorescent dyes in the presence of a pump field.

Laser inhibited diffusion in rhodamine-ethanol solutions

The diffusion of rhodamine-6G dye in ethanol is observed to be inhibited by optical pumping by a cadmium laser. The diffusion process is observed as a function of the solution temperature. The relative difference in diffusion coefficients with and without optical pumping is calculated. The effect is interpreted as being due to a stronger solvent-dye interaction in the first excited singlet state of rhodamine-6G.

The possibility of vibrational lasing in CD3F

Abstract Due to the unusual performance characteristics of the 206 μm emission of the CD3F optically-pumped molecular laser, a new lasing mechanism is proposed. The scheme is based on an inter-mode vibrational laser transition assignment: ν5(231)→ ν3(241).

Energy-transfer mechanisms in the CH 3 F–SF 6 optically pumped laser

The power of an optically pumped CH/sub 3/F laser operating on the 496-..mu..m line has been doubled with the addition of SF/sub 6/ without any corresponding increase in pump absorption. We believe that a near-resonant energy transfer between CH/sub 3/F and SF/sub 6/ followed by SF/sub 6/ deactivation is the mechanism responsible for the enhancement.